直接撸代码
%% ================ Part 1: Feature Normalization ================ %% Clear and Close Figures clear ; close all; clc fprintf('Loading data ...\n'); %% Load Data data = load('ex1data2.txt'); X = data(:, 1:2); y = data(:, 3); m = length(y); % Print out some data points fprintf('First 10 examples from the dataset: \n'); fprintf(' x = [%.0f %.0f], y = %.0f \n', [X(1:10,:) y(1:10,:)]'); fprintf('Program paused. Press enter to continue.\n'); pause; % Scale features and set them to zero mean fprintf('Normalizing Features ...\n'); [X mu sigma] = featureNormalize(X); % Add intercept term to X X = [ones(m, 1) X]; %% ================ Part 2: Gradient Descent ================ % ====================== YOUR CODE HERE ====================== % Instructions: We have provided you with the following starter % code that runs gradient descent with a particular % learning rate (alpha). % % Your task is to first make sure that your functions - % computeCost and gradientDescent already work with % this starter code and support multiple variables. % % After that, try running gradient descent with % different values of alpha and see which one gives % you the best result. % % Finally, you should complete the code at the end % to predict the price of a 1650 sq-ft, 3 br house. % % Hint: By using the 'hold on' command, you can plot multiple % graphs on the same figure. % % Hint: At prediction, make sure you do the same feature normalization. % fprintf('Running gradient descent ...\n'); % Choose some alpha value alpha = 0.01; num_iters = 400; % Init Theta and Run Gradient Descent theta = zeros(3, 1); [theta, J_history] = gradientDescentMulti(X, y, theta, alpha, num_iters); % Plot the convergence graph figure; plot(1:numel(J_history), J_history, '-b', 'LineWidth', 2); xlabel('Number of iterations'); ylabel('Cost J'); % Display gradient descent's result fprintf('Theta computed from gradient descent: \n'); fprintf(' %f \n', theta); fprintf('\n'); % Estimate the price of a 1650 sq-ft, 3 br house % ====================== YOUR CODE HERE ====================== % Recall that the first column of X is all-ones. Thus, it does % not need to be normalized. price = [1,1650,3]*theta; % You should change this % ============================================================ fprintf(['Predicted price of a 1650 sq-ft, 3 br house ' ... '(using gradient descent):\n $%f\n'], price); fprintf('Program paused. Press enter to continue.\n'); pause; %% ================ Part 3: Normal Equations ================ fprintf('Solving with normal equations...\n'); % ====================== YOUR CODE HERE ====================== % Instructions: The following code computes the closed form % solution for linear regression using the normal % equations. You should complete the code in % normalEqn.m % % After doing so, you should complete this code % to predict the price of a 1650 sq-ft, 3 br house. % %% Load Data data = csvread('ex1data2.txt'); X = data(:, 1:2); y = data(:, 3); m = length(y); % Add intercept term to X X = [ones(m, 1) X]; % Calculate the parameters from the normal equation theta = normalEqn(X, y); % Display normal equation's result fprintf('Theta computed from the normal equations: \n'); fprintf(' %f \n', theta); fprintf('\n'); % Estimate the price of a 1650 sq-ft, 3 br house %特征缩放 function [X_norm, mu, sigma] = featureNormalize(X) X_norm = X; mu = zeros(1, size(X, 2)); sigma = zeros(1, size(X, 2)); mu=X(:,1); sigma=X(:,2); mu = (mu-mean(mu))/std(mu); sigma = (sigma-mean(sigma))/std(sigma); X_norm=[mu,sigma]; end %梯度下降 function [theta, J_history] = gradientDescentMulti(X, y, theta, alpha, num_iters) m = length(y); % number of training examples J_history = zeros(num_iters, 1); for iter = 1:num_iters theta = theta -alpha/m*X'*(X*theta-y); J_history(iter) = computeCostMulti(X, y, theta); end %损失函数 function J = computeCostMulti(X, y, theta) J = sum((X*theta-y).^2)/(2*m); end %正则化求解theta function [theta] = normalEqn(X, y) theta = zeros(size(X, 2), 1); theta=pinv((X'*X))*X'*y end 这应该就是我这一下午的成就了嘻嘻嘻，排版太差了，下次要改